Efficient Synthesis of a C2‐Symmetric 2,2′‐Bipyridine‐α,α′‐1‐t–butyl‐diol Ligand by Stereoselective Double Hydrogen Transfer to a 2,2′‐Bipyridine‐diketone

An efficient and practical method was developed for the synthesis of C2‐symmetric 2,2′‐bipyridine‐α,α′‐1‐t‐butyl‐diol ligands. The disclosed synthesis involves the Ullmann homocoupling of a keto bromo‐pyridine under NiCl2/Zn/PPh3 conditions, followed by the stereoselective double hydrogen transfer to the obtained 2,2′‐bipyridine‐diketone using RuII Noyori–Ikariya catalysts. This approach allowed the successful synthesis of 2,2′‐bipyridine‐α,α′‐1‐t‐butyl‐diol, i.e (S,S)‐Bolm's ligand, with a quantitative yield and an excellent stereoselectivity (ee>99.5 %, de>99.5 %), with an overall yield of 69 % from easily accessible starting materials. An efficient and practical method was developed for the synthesis of C2‐symmetric 2,2′‐bipyridine‐α,α′‐1‐t‐butyl‐diol ligands. This new approach enabled the successful synthesis of 2,2′‐bipyridine‐α,α′‐1‐t‐butyl‐diol with an overall yield of 69 % from easily accessible starting materials. By utilizing the power of creating two independent stereocenters, this synthesis led to excellent stereoselectivity (ee>99.5 %, de>99.5 %) without the need for recrystallization of any intermediate enantiomers during the synthesis.